Cup drawing apparatus



23, 1952 R. E. sLATl-:R

CUP DRAWING APPARATUS Filed oct. '7, 1948 o 0 Ac D u 0 0 0 o 0 5 2 3 w M0 0 d 6 9 0 0 0 0 0 0 0 M l INVENTOR. /PA YMoA/ 5 SLA 727? A rra/wf YsPatented Sept. 23, 1952 CUP DRAWING APPARATUS Raymond E. Slater, NewRochelle, N. Y., assignor to Remington Arms Company, Inc., Bridgeport,

Conn., a corporation of Delaware Applicationoctober 7, 1948, Serial No.53,298

This invention `relates to apparatus for Vthe forming of cup-likearticles of manufacture and has particular reference to a punch and dieset arranged to form such articles by a drawing op' eration and tosimultaneously trim the mouth portion thereof to prescribed dimensions.

This application is a continuation-in-part of my copending applicationSerial Number 598,083, filed June 7,1945, entitled Die, and nowabandoned.

It is an object of my invention to provide a die in which a cup'may bedrawn by a draw punch to a desired depth and wall thickness, and whereinthe metal at themouth edge vof the drawn cup, which has usually beentrimmed off in a subsequent operation,'is removed in the die at apredetermined fracture point, the resultant cup having a predeterminedheight dimension and a substantially smooth trimmed edge.

In theusual cup drawing die the entrance to the land of the die isdefined by a generatrix at a relatively small angle with the axis of thedie land and is of substantial depth, so that as the wall of the cup isdrawn the metal in the entrance portion of the die for a considerable`distance above the die land assumes the cross-sectional shape .of thespace between the entrance portion and the punch, being graduallyreduced and drawn through the land and producing at the upper edge ofthe cup an irregular edge which is later removed in a suitable trimmingor cutoff machine. It has also'been a relatively common practice tol usewith dies ofthis type a punch having a shoulder closely fitting the dieland which shears or. pinches oii the upper portion of the cup as theshoulderpasses into the land of the die. With such close fitting toolsthere is always a tendency for apart of the edge of the cup to beextruded into the small clearance between punch shoulder'and die, withthe result that the edge of the trimmed cup will be surmounted with anumberof paper thin ypinnacles or weblike protuberances. If thesepinnaclesare permitted to remain on a shot shell cup they may be turnedinto the paper body ,on linal assembly, causing frequent cutoifs onflringas a result of the localized weakness of the body. The avoidanceof cutofs has required that pinch-off work for shot shells be tumbled insawdust to break off the pinnacles, and the rough handling incident tolthe tumbling operation has resulted in the appearance of a multitude ofnew defects of one sort or another.

It is proposed in the present invention to provide a die having anentrance portion which is Claims. (Cl. 205-7) 2 deiined by -ageneratrix` at a relatively largeangle with the axis of the die land, sothat it does not outwardly co-nne the metal, and which therefore permitsthe formation by iianging means on the punch of a flange at the mouthedge of the drawn cup, and it is further proposed according to theinvention to utilize this nange formation for the purpose of trimmingthe drawn cup at a predetermined point in the drawing operation.

In the drawing of tubes or cups, if the metal being drawn is at any timeso treated that the forces imposed thereon exceed the strength'of themetal a break will occur, and this canhappen in either of two ways. Afracture .can be started in the metal and the forces drawing the metalrelied upon to complete the break, orthe thickness of the metal can beso reduced that, presuming a relatively constant drawngfo-rce, theultimate tensile strength of the Wall of the tube is exceeded and thebreak occurs. If this breaking can be predetermined as to occurrence andlocation, a result'simlarto va cutoff occurs, the tube or cup can bedrawn to a desired length, and surplus metal scrapped'by breaking it ofand discarding. In the drawing operation, the resistance to the movementof the draw punch is developed against the face of the entry by themetal which has not as yet been sizedto the diameter oi the die land,and as the forceof the punch is, to a large degree, exerted through thenose of the punch the metal passing the die land is under considerabletension. It is proposed in the inventionto provide means whereby at apre'- determined point inthe movement of the .punch the now' of metalthrough the'die land is sharply restricted by the shoulder on the punch,so that this restricted metal must thereupon carry the full tensile loadof the piece being drawn and, as a result, is stressed beyond itsultimate tensile strength.

It is further proposed to so shape the shoulder on the punch and thecorner of the die land as to provide symmetrical opposed notchescontiguous to the stressed metal, with the result that a combination oftensile forces, directly from the pull of drawing, and secondarily fromthe notch effect, produce a fracture in the metal, causing the flangeformed at the upper end of the tube to .be separated as a scrapring,.the fracture line of the drawn piece being ata predetermined pointand constituting a substantially smooth trimmed edge. Since such afracture is analogous to that which occurs when a notched tensile testspecimen is fractured, the necking down which follows the exceeding ofthe elastic limit will con 3 tribute materially to the production of asmooth outwardly and inwardly beveled edge.

The exact nature of the invention as well as other objects andadvantages thereof will more clearly appear from consideration of thefollowing specification referring to the attached drawing, in which:

Fig. l is a vertical sectional view showing a punch engaged with a cupwhich is in the process of being drawn in a die of the preferred form.The relative wall thickness of the cup is exaggerated for clarity inillustration. Fig. 2 is a similar view at a later point in the drawingcycle where the shoulder on the punch has commenced to cooperate withthe die corner to reduce the cross section of the cup.

Fig. 3 is a similar View after the cup has been fractured from the scrapring along the line defined by the reduction in thickness.

Fig. 4 is an enlarged, partial vertical sectional view illustrating theshape of the edge of the cup and of the scrap ring in the zone of thefracture.

Fig. 5 is a graphical diagram on which punch shoulder angle is plottedagainst die entrance angle. The closed figure surrounds an area withinwhich work of uniformly high quality is produced with a compressivereduction of the cup wall thickness at the cutoff line of only 75% ofthe total wall thickness.

Fig. 6 is a similar figure showing the conditions at a reduction of only62.5%, and

Fig. 7 is a similar figure showing conditions when the cup wallisreduced only 50% prior to fracturing.

Referring to the drawing, it will be seen that the first three figuresillustrate successive steps in the drawing and trimming of a cup-shapedworkpiece I0. In accordance with the usual drawing procedure, theworkpiece I has been, in a previous step, positioned in alignment withthe draw punch Il which, upon descending, enters into the workpiece andforces it into the draw die l2. The forces acting on the punch Il aretransmitted through the nose of the punch to the bottom of the workpiecel0 and serve in the usual manner to draw out the side walls thereof,increasing the height of the cup and sizing the walls thereof to matchthe space between the nose portion I3 of the punch and the land I4 ofthe die. As the resistance to the drawing of the workpiece is developedagainst the conical entrance l of the die, it follows that the sideWalls of the workpiece are under a heavy tensile load. As the punchdescends, the gripping action of the die entrance is enhanced by theaction of the shoulder I6 on the punch which acts to flare the mouth ofthe workpiece into a ange engaging a greater area of the die entrancecone than would otherwise be the case. This is the condition illustratedin Fig. 1 with the flanged mouth Illa of the workpiece securely grippedin the die entrance and high tensile loads imposed on the wall of theworkpiece.

As shown in Fig. 2, the continued advance of the punch causes theshoulder thereon to approach the corner between the die land and theconical entrance portion of the die, with the result that a sharplydefined annular zone of reduced thickness will be formed in theworkpiece wall. This zone will be at its minimum thickness when theshoulder is in opposition to the corner of the die land, and at thistime the flange Ia of the workpiece will be most securely held. It istherefore inevitable that the continued application of tension to theworkpiece will result in the development of a fracture in the notchedwall in exactly the same manner as a notched tensile test specimenfractures in a testing machine. This condition is illustrated in Fig. 3,and in Fig. 4 an enlarged cross section shows the typical necking-downand fracture of a notched tension fracture.

The magnitude and rate of development of the forces involved are, to alarge extent, dependent upon the clearance between punch and die and yonthe relative angles of the die entrance throat and the shoulder of thepunch. Since both die entrance throat and punch shoulder can be mostconveniently formed as conical surfaces concentric with the axis of thedie land, it is convenient to define the angles involved by reference tothe axis of the die land or the axis of the punch. For example, in thefollowing discussion, a die throat which is of frusto-conical shape andis defined by an included angle of could be generated by a line whichmakes an angle of 45 with the axis of the die land and will be spoken ofas a 45 die. The same practice will be followed in regard to theshoulder on the punch.

In an extensive study of the mechanism involved in single operation drawand cutoff work, it has been found that, when the extremely closeclearances characteristic of the prior art are maintained between apunch shoulder and the die land, the major considerations are found inmaintaining the close clearance and sharpness of the punch shouldernecessary to cut through the Wall of the workpiece or to exert ashearing or pinching action thereon. The punches employed have beenuniformly provided with a 90 or square, sharp shoulder and die entranceangles have varied from curved throats tangent to the die land tofrusto-conical surfaces generated by a line making a fairly low anglewith the axis of the die land. Applicant has found that die entranceangles materially greater than 42 are not useful with any range ofclearances or with any shape of punch shoulder since the resistance todrawing of the cup wall is so great that the punch will tear the bottomout of the cup or pull the wall apart at some indefinite pointdetermined by slight irregularities in metal composition or condition.Similarly, applicant has found that die entrance angles lower than 17,when used with punches having little or no clearance in the die land,invariably result in the characteristic edge contour of the priorpinch-olf practice. The trimmed edge is characterized by a multiplicityof small webs and pinnacles extruded from the severed edges by the highradial pressures involved. With such dies, tools having medium or largeclearance fail to cut off at all. Within the operative range ofclearances any damage to the sharp corner of the punch quickly resultsin an unacceptable product.

Within a range of die entrance angles between about 17 and 42, applicanthas found that even when the clearance between punch shoulder corner anddie land corner is equal to 25% of the thickness of the cup wall, asdistinguished from a shearing or pinch-off clearance, uniformlyexcellent work may be obtained throughout almost the entire range whenthe punch shoulder angle is varied from substantally 15 to substantially60. This condition is illustrated in Fig. 4. As might be expected, thecritical nature of die throat and punch shoulder angles becomesincreasingly apparent when attempts are made to operate with greaterclearances between punch shoulder corner and die land corner. Figs. 6and acume 7 illustrate the conditions which prevail when the weboftheworkpiece in thenotched zone was respectively 37.5% and 50% of thethickness of' the cup wall in the region below the fracturev line.Although thel same carefully controlled tests were not carried out todetermine the absolute limit ofv clearance which may be employed,instances arev known in which excellent `cutois were obtainedwhen theminimum thickness ofthe reduced zone approached two-thirds the thicknessof the cup wall. The necessary condition appears to be one in whichpunch shoulder and die entrance throat are substantially parallel`frusto conical surfaces, each being dened by a line generatrlx makingan angle with the axis of the die land within arange between 17 and 42Vwith the optimum angles for both punch and die being near or slightlybelow 30.

The importance of starting initially with a fairly high clearance willbe better appreciated with the realization that it is extremelydifficult to keep punches and dies in absolute alignment Aand that nopress feeding device is infallible. In

production operations concentricity of the workpiece is to aconsiderable degree dependent upon the self-centering action of theworkpiece 'encountering the die throat and centering the punch either byslight flexing of the punch shank or shifting of the press head upon itsguide-ways. If the feeding device should fail, punch and die may thenmake direct contact which, in the case of a close clearance, squareshouldered punch, may, and usually does, result in deformation of thepunch shoulder edge with the subsequent production of draw componentshaving a burr at this point. The greater the clearances the lessliability to tool contact due to misalignment, and when the punchshoulder and die entrance are formed on mating angles the damage fromdirect contact of tools will often be avoided and always minimized.

A further important advantage of the use of the optimum tool design willbe found in the greater wear which may be obtained from such tools.Starting with a matching punch and die of the optimum angles and with aclearance which is a minimum consistent with the avoidance of directtool contact, as noted above, the tools may be run until the diametersof the cup are no longer acceptable without failure to produce goodcutois and accurate sizing as to length of the cup wall. In fact, theeiects of wear on the punch shoulder and on the corner of the die landare, to a considerable extent, self-compensating for the eiective anglestend to change together and to maintain their parallel relationship.Thus, the zone of minimum thickness remains sharply defined and atsubstantially the same distance from the nose of the punch producing asubstantially constant height of cup. In actual production use toolsproduced in accordance with this invention have a working life manytimes greater than the low clearance, square punch shouldered toolsemployed for pinch-off or shear cutoi work.

The preceding discussion is intended to be illustrative only of certainpreferred embodiments of my invention and is not intended to serve as alimitation thereon to any greater extent than set forth in the claimsappended hereto.

I claim:

1. Apparatus for the forming and trimming of metallic cups comprising adraw die having a die land and a frusto-conical entrance throat having aleast diameter substantially equal to 6. the inside diameter ofthe dieland and leading thereinto, 'saldi irusto-cori-ical throat being definedbya line generatrix'forming an angle with theaxi'sy ofthe die land ofbetween 17 and 42; and a draw punch cooperating with said die having' agenerally cylindrical nose portion constructedl andv arranged to engagea cupped workpiece and to draw same through the die land, said punchbeing formed at` the upper end oi? said nose portion with adiametrically enlarged shoulder, the radial clearance between the majordiameter of said'shoulder and the die land beingmore than one-'fourth ofand less than one-half ofthe radial clearance betweenvthe nose portionof the punch and the die land.

2. Apparatus for the 'forming and trimming of metallic cups comprising adraw die having a die land and a "frusto-conical entrance throat having'a least diameter substantially equal to the inside diameter ofthe dieland and leading thereinto, said frusto-ccnical throat being defined bya line generatrix forming an angle with theaxis of the die land ofbetween 17 and 42; anda draw punch cooperating with said die having agenerally cylindrical nose portion constructed'and arranged to engage acupped workpiece and yto draw same through the die land, said punchbeing formed at the upper end of said nose portion'withA an upwardly andoutwardly enlarged frusto-conical shoulder the radial clearance betweenthe major diameter of said shoulder and the die land being more thanone-fourth of and less than one-half of the radial clearance between thenose portion of the punch and the die land.

3. Apparatus for draw forming metallic cupshaped workpieces and trimmingsuch workpieces to a predetermined height comprising a draw die having adie land of generally cylindrical form and substantially the diameter ofthe finished workpiece, and a die entrance throat of substantiallyfrustro-conical shape having a least diameter substantially equal to theinside diameter of said die land and leading thereinto, said throatbeing defined by a line generatrix making an angle with the axis of thedie land of between 17 and 42; and a draw punch cooperating with saiddie and having a generally cylindrical nose portion of substantially thediameter of the inside of the iinished workpiece and of substantiallythe same length as the depth of said finished workpiece, said noseportion terminating in an enlarged frusto-conical shoulder defined by aline generatrix making an angle with the axis of the punch of between 17and 42 with the axis of the die land, the radial clearance between themajor diameter 0f said shoulder and the die land being equal to or morethan one-fourth of and less than one-half of the radial clearancebetween the nose portion of the punch and the die land.

4. Apparatus for draw forming metallic cupshaped workpieces and trimmingsuch workpieces to a predetermined height comprising a draw die having adie land of generally cylindrical form and substantially the diameter ofthe finished workpiece, and a die entrance throat of substantiallyfrustro-conical shape having a least diameter substantially equal to theinside diameter of said die land and leading into said land, said throatbeing defined by a line generatrix making an angle with the axisof thedie land of between 17 and 42; and a draw punch cooperating with saiddie and having a generally cylindrical nose portion of substantially thediameter of the inside of the finished workpiece and of substantiallythe same length as the -depth of said nished workpiece, said noseportion terminating in an enlarged frustro-conical shoulder dened by ageneratrix which intersects the axis of the punch at substantially thesame angle as the angle between the line generating said die throat andthe axis of the die land, whereby said frusto-conical shoulder and saidfrustoconical die throat will bel dened by ysubstantially parallelsurfaces, vthe radial' clearance between the major diameter of saidshoulder and the die land being betWeen-one-fcurth and one-half of theradial clearance between the nose portion of the punch and the die land.

5. Apparatus for draw forming metallic cupshaped workpieces and trimmingsuch workpieces to a predetermined height comprising a draw die having adie land of generally cylindrical form and substantially the diameter ofthe finished 20 workpiece, and a die entrance throat of Substantiallyfrusto-conical shape having a least diameter substantially equal tc theinside diameter of said die land and-leading into said land, said throatbeing dened by a line generatrix making an angle with the axis of-thedie land of between 23 and 32; and a draw punch cooperating with saiddie and having a generally cylindrical nose portion ofl substantiallythe 8 diameter of the inside of the finished workpiece and ofsubstantially the same length as the depth of said iinished workpiece,said nose portion terminating in an enlarged frusto-conical shoulderdened by a generatrix which intersects the axis of the punch atsubstantially the same angle as the angle between the line generatingsaid die throat and the axis of the die land, whereby saidfrusto-conical shoulder and said frusto-conical die throat will be denedby substantially parallel surfaces, the radial clearance between themajor diameter of said shoulder and the die land being betweenone-fourth and one-half of the radial clearance between the nose portionof the punch and the die land.

v RAYMOND E. SLATER.

REFERENCES CITED The following references are of record in the file ofthis patent:

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